Weight loss is a frequently recommended treatment for obese patients with OSA, but the data to support this recommendation are not available. The lack of randomized trials, the study of predominantly male samples, and the absence of any long-term data leave physicians and patients unsure about the clinical utility of weight loss for obese OSA patients. We propose to extend our initial 2-year assessment of obese patients with OSA and T2DM in the Sleep AHEAD who were randomly assigned to weight loss or usual care (no weight loss) treatment conditions. Our assessment of patients at baseline, 1 and 2 years and the proposed 4 years will allow us to examine the relationship between bidirectional weight change and SDB over time. We will also examine the role of neck and abdominal fat distribution in mediating the effects of weight loss on SDB. Finally, we will assess the impact of changes in weight and changes in AHI on changes on three outcomes that are clinically relevant (glycemic control, inflammation, and blood pressure) in obese patients with OSA and T2DM. Our sample is unique for its large number (n= 296) of obese patients with OSA and T2DM, nearly equal numbers of males (40 percent) and females (60 percent) and subjects who are already enrolled in Look AHEAD. This study provides a randomized controlled trial of a weight loss intervention, using state- of-the-art treatment, at no cost to the ancillary study. We believe that the systematic study of this cohort will provide clinically meaningful information about the effects of weight loss for obese patients with both T2DM and OSA, as well as expand our fund of knowledge about the roles of short and long-term changes in weight and changes in AHI glycemic control, inflammation, and blood pressure. [unreadable] [unreadable] [unreadable]